1. Field of the Invention
Embodiments in accordance with the present disclosure are directed to integrated circuits containing non-volatile memory cell arrays and particularly those arrays incorporating passive element memory cells.
2. Description of the Related Art
Materials having a detectable level of change in state, such as a resistance or phase change, are used to form various types of non-volatile semiconductor based memory devices. For example, some materials (e.g., carbon) can be switched between low and high resistance states. These types of materials can be used to form re-writable memory cells. Multiple levels of detectable resistance in materials can further be used to form multi-state devices which may or may not be re-writable.
Materials having a memory effect such as a detectable level of resistance are often placed in series with a steering element to form a memory device. Diodes or other devices having a non-linear conduction current are typically used as the steering element. In many implementations, a set of word lines and bit lines are arranged in a substantially perpendicular configuration with a memory cell at the intersection of each word line and bit line. Two-terminal memory cells can be constructed at the intersections with one terminal (e.g., terminal portion of the cell or separate layer of the cell) in contact with the conductor forming the respective word line and another terminal in contact with the conductor forming the respective bit line.
One type of diode that might be used for the steering element is a metal insulator metal diode. Metal insulator diodes may have more than one insulating layer. Thus, as the term is used herein “metal-insulator diode” includes diodes with one or more insulator layers. For example, one configuration is a metal-insulator-insulator-metal diode (MIIM diode). Unfortunately, forming MIIM diodes that have good “on current” and rectification ratios is challenging. As scaling of devices to smaller feature sizes continues, there is a need for diodes with good rectification behavior and smaller aspect ratios.
Moreover, it is desirable that the techniques used to form switchable memory elements are compatible with techniques used to form steering elements, such as MIIM diodes.